CN107851736B

CN107851736B - N-type doped semiconductor material comprising a polar matrix and a metal dopant

Info

Publication number: CN107851736B
Application number: CN201680043294.3A
Authority: CN
Inventors: 乌尔里希·登克尔; 卡斯滕·洛特; 沃洛季米尔·森科维斯基; 托马斯·卡里兹
Original assignee: NovaLED GmbH
Current assignee: NovaLED GmbH
Priority date: 2015-06-23
Filing date: 2016-06-22
Publication date: 2020-06-05
Anticipated expiration: 2036-06-22
Also published as: JP2021145144A; JP2021132218A; KR102581921B1; WO2016207228A1; US20180182960A1; WO2016207229A1; CN107851736A; KR102581918B1; KR20180019731A; KR20180019224A; JP2018527740A; CN107851735A; CN107851735B; US10749115B2; JP7443286B2; JP2018524812A; US20190036032A1

Abstract

The present invention relates to a semiconducting material comprising (i) an electropositive element in substantially elemental form selected from alkali metals, alkaline earth metals, rare earth metals and transition metals, and (ii) at least one first compound which is a compound comprising at least one polar group selected from a phosphine oxide group or an oxadiazole group; a method of manufacturing the semiconductor material; an electronic device comprising a cathode, an anode and said semiconductor material.

Description

N-type doped semiconductor material comprising a polar matrix and a metal dopant

Technical Field

The present invention relates to organic semiconductor materials having improved electrical properties, to a process for their preparation, to electronic devices utilizing the improved electrical properties of the semiconductor materials of the invention, in particular devices comprising the organic semiconductor materials in an electron transport layer and/or an electron injection layer, and to electron transport matrix compounds which can be applied in the semiconductor materials of the invention.

Background

Organic Light Emitting Diodes (OLEDs) have gained prominence in electronic devices comprising at least components based on materials provided by organic chemistry. Since their display in 1987 (c.w.tang et al, appl.phys.lett. (applied physical bulletin) 51(12),913(1987)), OLEDs have evolved from promising candidates to high-end commercial displays. OLEDs comprise a series of thin layers made substantially of organic materials. The thickness of the layer is typically 1nm to 5 μm. The layer is typically formed by vacuum deposition or from a solution, for example by spin coating or jet printing.

After charge carriers are injected in the form of electrons from the cathode and holes from the anode into the organic layers arranged therebetween, the OLED emits light. Charge carrier injection is achieved based on an applied external voltage, followed by the formation of excitons in the light emitting region and the radiative recombination of these excitons. At least one of the electrodes is transparent or translucent, in most cases in the form of a transparent oxide, such as Indium Tin Oxide (ITO), or a thin metal layer.

Among the matrix compounds used in the light-emitting layer (LEL) or the Electron Transport Layer (ETL) of OLEDs, compounds comprising at least one polar group selected from phosphine oxides and diazoles play an important role. The reason why such polar groups often significantly improve the electron injection and/or electron transport properties of semiconductor materials is not fully understood. It is believed that the high dipole moment of the polar group plays a positive role. Particularly recommended for such use are triarylphosphine oxides comprising at least one fused aromatic or heteroaromatic group directly linked to a phosphine oxide group, see for example JP 4876333B 2. Of the diazole groups, in particular phenylbenzimidazole groups, have been widely used for the design of new electron transport matrix compounds, such as TPBI described in US 5645948, and some compounds comprising a benzimidazolyl moiety linked to other moieties comprising delocalized pi electrons in two or more aromatic or heteroaromatic rings are nowadays considered as industrial standards, such as compound LG-201 (e.g. US 6878469)

Since the 90 s of the 20 th century, charge-transporting semiconductor materials have been known, for example from US 5093698A, for electrical doping to improve their electrical properties, in particular electrical conductivity. A particularly simple method for n-type doping in ETLs prepared by thermal vacuum deposition (which is currently the standard method most commonly used, for example, in the industrial manufacture of displays) is to evaporate the matrix compound from one evaporation source and the highly electropositive metal from another evaporation source and co-deposit them on a solid substrate. As n-dopants useful in triarylphosphine oxide matrix compounds, alkali and alkaline earth metals are recommended in JP 4725056B 2, with cesium being successfully used as a dopant in the given examples. Indeed, cesium as the most electropositive metal offers the broadest freedom in the choice of matrix material, and this may be the reason why only cesium is chosen as n-type doping metal in the cited document.

For industrial use, cesium has several serious drawbacks as a dopant. First, it is a very reactive, moisture sensitive and highly air sensitive material, which makes it difficult to handle and incurs significant additional costs for mitigating the high levels of safety and fire hazards inevitably associated with its use. Second, its relatively low normal boiling point (678 ℃) indicates that it may be highly volatile under high vacuum conditions. In fact, less than 10 is used in Vacuum Thermal Evaporation (VTE) industrial plants^- ²At Pa, the cesium metal has already significantly evaporated at slightly elevated temperatures. Considering that typical matrix compounds used in organic semiconductor materials are below 10^-2The evaporation temperature at a pressure of Pa is typically between 150-400 ℃, and avoiding uncontrolled cesium evaporation, which leads to undesired deposition of colder parts contaminating the whole apparatus (e.g. parts blocking thermal radiation from organic matrix evaporation sources), is a very challenging task.

Several approaches have been published to overcome these drawbacks and to achieve industrial applicability of cesium for n-type doping in organic electronic devices. For safe handling, it is preferred that cesium can be supplied in a sealed enclosure that can only be opened within a vacuum evaporation source during heating to operating temperature. This technical solution is provided, for example, in WO 2007/065685, but it does not solve the problem of high volatility of cesium.

US 7507694B 2 and EP 1648042B 1 provide another solution in the form of cesium alloys which melt at low temperatures and show a significantly reduced cesium vapor pressure compared to pure metals. In WO2007/109815 at about 10^-4Bismuth alloys that release cesium vapor at pressures of Pa and temperatures up to about 450 ℃ represent another alternative. However, all of these alloys are still highly sensitive to air and moisture. Moreover, this solution has the additional drawback that the vapour pressure on the alloy during evaporation varies as the cesium concentration decreases. This creates a new problem of properly controlling the deposition rate, for example by programming the temperature of the evaporation source. To date, Quality Assurance (QA) concerns about the robustness of such processes on an industrial scale have hindered the wider application of such technical solutions in large-scale production processes.

A possible alternative to Cs doping is a highly electropositive transition metal complex such as W₂(hpp)₄Its ionization potential is as low as cesium and its volatility is comparable to that of common organic matrices. Indeed, these complexes, which were first disclosed as electrical dopants in WO2005/086251, are very effective for most electron transport matrices, with the exception of some hydrocarbon matrices. Despite their high air and moisture sensitivity, these metal complexes provide satisfactory n-type doping solutions for industrial use if supplied in housings according to WO 2007/065685. Their main drawbacks are their high price due to the relative chemical complexity of the ligands involved and the need for multistep synthesis of the final complex, as well as the additional costs due to the need to use protective shells and/or QA and logistic problems associated with shell recycling and refilling.

Another alternative is a strong n-type dopant generated in situ in the doped matrix from a relatively stable precursor by additional energy provided, for example, in the form of Ultraviolet (UV) or visible light of appropriate wavelength. Compounds suitable for such solutions are provided, for example, in WO 2007/107306A 1. However, the most advanced industrial evaporation sources require materials with very high thermal stability, allowing them to be heated to the operating temperature of the evaporation source without any decomposition during the whole operating cycle of the source loaded with the material to be evaporated (for example at 300 ℃ for one week). It has heretofore been a real technical challenge to provide such long-term thermal stability for organic n-type dopants or n-type dopant precursors. Moreover, the complex arrangement of the production equipment of the additional energy supply (by in situ activation of the dopant precursor deposited in the matrix) that has to ensure reproducible achievement of the definition and reproducibility of the desired doping level is a potential source of further technical challenges and other CA problems in mass production.

Yook et al (Advanced Functional Materials, 2010,20, 1797-. This compound is known to decompose to metallic cesium and elemental nitrogen upon heating above 300 ℃. However, this approach is hardly applicable in contemporary industrial VTE sources, because such heterogeneous decomposition reactions are difficult to control on a larger scale. Furthermore, the release of nitrogen as a by-product in this reaction carries a high risk, especially at the higher deposition rates required in large scale production, the expanding gas will eject solid cesium azide particles from the evaporation source, resulting in such a high defect count in the deposited layer of doped semiconductor material.

Another alternative to n-type electrical doping in an electron transporting matrix is doping with metal salts or metal complexes. The most common example of such a dopant is lithium 8-hydroxy-quinoline (LiQ). It is particularly advantageous in matrices comprising phosphine oxide groups, see for example WO 2012/173370 a 2. The main disadvantage of metal salt dopants is that they substantially only improve electron injection into adjacent layers without increasing the conductivity of the doped layer. Thus, its use to reduce operating voltage in electronic devices is limited to rather thin electron injection or electron transport layers and hardly allows tuning of the optical cavity, for example by using an ETL with a thickness greater than about 25nm, as is possible with redox doped ETLs with high conductivity. Furthermore, metal salts generally cannot act as electrical dopants in cases where it is important to generate new charge carriers in a doped layer, for example in a charge generation layer (CGL, also known as a p-n junction) required for the function of a tandem OLED.

For the reasons described above, and especially for electrical doping in ETLs with thicknesses greater than about 30nm, current technical practice prefers lithium as the industrial redox n-type dopant (see, e.g., US 6013384B 2). This metal is relatively inexpensive and differs from other alkali metals in that it is somewhat less reactive, and in particular significantly less volatile (normal boiling point about 1340 ℃) so that it evaporates at temperatures of 350 ℃ and 550 ℃ in the VTE equipment.

Li is enabled to dope most common types of electron transport matrices purely by its high n-type doping capability, but this metal still has a high degree of reactivity. It reacts even with dry nitrogen at ambient temperature and for its use in a highly reproducible manufacturing process that meets contemporary industry QA standards, it must be stored and handled exclusively under high purity inert gas. Moreover, if Li is co-evaporated with a matrix compound having an evaporation temperature in the range of 150-.

Many documents propose almost any known metallic element as an alternative n-type dopant, including Zn, Cd, Hg with weak reducibility and high volatility, Al, Ga, In, Tl, Bi, Sn, Pb, Fe, Co, Ni with weak reducibility or even noble metals such as Ru, Rh, Ir and/or refractory metals with the highest known boiling point such as Mo, W, Nb, Zr (see for example JP 2009/076508 or WO 2009/106068). Unfortunately, not only in the two documents cited here as examples, but also throughout the scientific and patent literature, there is virtually no evidence that some of these proposals have been experimentally tested.

More specifically, even WO2009/106068, which mentions not only all conceivable dopants, but also real efforts requiring all known metalloid elements as n-dopants in organic electronic devices (due to their allegedly suitability for pyrolysis by gaseous precursor compounds in heated nozzles), does not bring any numerical value to record the physical parameters of the allegedly produced doping materials and/or the technical properties of the allegedly produced devices.

On the other hand, US2005/0042548 published before the priority date of WO2009/106068, in paragraph 0069 (i.e. see page 7, the last two lines in the left column and the first three lines in the right column), teaches that iron pentacarbonyl can be used for n-type doping in organic ETMs if it is activated by UV radiation that decomposes out carbon monoxide ligands. The coordinately unsaturated iron compound then reacts with the matrix, which leads to the doping effect observed. According to this prior art showing that the metal carbonyl compounds used in the claimed working examples of WO2009/106068 are known n-type dopants in organic matrices if activated by an additional energy supply, it seems quite likely that if the applicant of WO2009/106068 does obtain any doping effect in the target bathocuproine layer by means of a jet whose iron pentacarbonyl flows through a ceramic nozzle (see last paragraph of the german text on page 12 of the cited PCT application) which is electrically heated to incandescence, this effect is caused by the same coordinatively unsaturated iron carbonyl complexes produced by UV radiation in US2005/0042548, rather than the elemental iron they propose. This suspicion is further supported in the fourth paragraph on page 13 of the cited PCT application which teaches that the same result can be obtained with a cold nozzle if the iron pentacarbonyl stream is irradiated with an infrared laser with a wavelength that coincides with the absorption frequency of the CO groups in the iron pentacarbonyl complex. Here, it is more likely that laser activation does not produce a bare metal atom or cluster of metal atoms, but rather a reactive, coordinately unsaturated iron complex still bearing some carbonyl ligands, similar to the reactive complex formed by activation with UV light.

Although metals having strongly negative standard redox potentials, such as alkaline earth metals or lanthanides, are also described as alternative n-type dopants in addition to alkali metals, basically in every document dealing with redox n-type doping, it proves to be very rare to record n-type doping with any metal other than alkali metals.

Magnesium is much less reactive than alkali metals. It reacts very slowly even with liquid water at normal temperature, it maintains metallic luster in air and it does not increase in weight within months. It can be considered to be almost air stable. Furthermore, it has a low normal boiling point (about 1100 ℃), and VTE processing in the optimal temperature range for co-evaporation with organic substrates is very promising.

On the other hand, the authors of the present application demonstrated in the screening with several tens of the most advanced ETMs that Mg does not have sufficient doping strength for a normal ETM that does not contain strongly polar groups such as phosphine oxide groups. The only advantageous results have been achieved in OLEDs comprising a thin electron-injecting layer consisting of a specific kind of triarylphosphine oxide matrix doped with magnesium (comprising special tripyridyl units designed to chelate metals), as shown in EP 2452946 a 1. Although the exemplary matrix tested with magnesium in EP 2452946 a1 has structural specificity and very advantageous (in terms of its LUMO level, which is quite deep at vacuum level in absolute energy scale) dopability, the positive results achieved with such n-type doped semiconductor materials further encourages research focused on n-type doping with substantially air-stable metals.

It is an object of the present invention to overcome the disadvantages of the prior art and to provide an efficient n-doped semiconductor material, preferably using a substantially air-stable metal as n-dopant, in particular relative to ferrocene, compared to the electrochemical redox potential (which is in a simple linear relationship with the LUMO level and is easier to measure than the LUMO level itself)

The/ferrocene reference has an ETM that is more negative than about-2.25V, in an ETM having a Lowest Unoccupied Molecular Orbital (LUMO) level that is closer to the vacuum level.

It is another object of the present invention to provide alternative metal elements that are substantially air stable and can be successfully embedded (preferably by standard VTE processes and using contemporary evaporation sources) in electrically doped semiconductor materials used in electronic devices.

It is a third object of the present invention to provide a method of fabricating the semiconductor material using a substantially air stable metal as an n-type dopant.

It is a fourth object of the invention to provide a device with better characteristics, especially a device with a low voltage, and more particularly an OLED with a low voltage and a high efficiency.

A fifth object of the present invention is to provide novel matrix compounds suitable for use in the semiconducting material according to the present invention.

Disclosure of Invention

The object is achieved by a semiconductor material

The semiconductor material comprises:

(i) an electropositive element in substantially elemental form selected from the group consisting of alkali metals, alkaline earth metals, rare earth metals, and transition metals of the fourth period of the periodic table having a proton number of 22, 23, 24, 25, 26, 27, 28, 29, and

(ii) at least one first compound being a compound comprising at least one polar group selected from a phosphine oxide group or an oxadiazole group, wherein

The first compound is a substantially covalent compound which contains no conjugated system of delocalized electrons, or contains a conjugated system of delocalized electrons with less than 10 conjugated delocalized electrons, and the value of the reduction potential of the first compound is more negative than the value obtained for tris (2-benzo [ d ] thiazol-2-yl) phenoxyaluminum, preferably more negative than 9,9',10,10' -tetraphenyl-2, 2 '-bianthracene or 2, 9-bis ([1,1' -biphenyl ] -4-yl) -4, 7-diphenyl-1, 10-phenanthroline, more preferably more negative than 2,4,7, 9-tetraphenyl-1, 10-phenanthroline, even more preferably more negative than 9, if measured by cyclic voltammetry under the same conditions, 10-bis (naphthalen-2-yl) -2-phenylanthracene is more negative, even more preferably more negative than 2, 9-bis (2-methoxyphenyl) -4, 7-diphenyl-1, 10-phenanthroline, even more preferably more negative than 9,9' -spirobis [ fluorene ] -2, 7-diylbis (diphenylphosphine oxide), even more preferably more negative than 4, 7-diphenyl-1, 10-phenanthroline, even more preferably more negative than 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene, most preferably more negative than pyrene and still preferably more negative than the values obtained for [1,1' -binaphthyl ] -2,2' -diylbis (diphenylphosphine oxide).

It is understood that "substantially covalent" refers to compounds comprising elements that are bound together primarily by covalent bonds. Examples of substantially covalent molecular structures may be organic compounds, organometallic compounds, metal complexes comprising polyatomic ligands, metal salts of organic acids. In this sense, the term "substantially organic layer" is understood to mean a layer comprising a substantially covalent electron transport matrix compound.

It is also to be understood that the term "substantially covalent compound" encompasses materials that can be processed by common techniques and equipment used to fabricate organic electronic devices, such as vacuum thermal evaporation or solution processing. It is clear that pure inorganic crystalline or glassy semiconductor materials, such as silicon or germanium, which cannot be prepared in the equipment of organic electronic devices due to extremely high evaporation temperatures and solvent insolubility, are not covered by the term "substantially covalent compounds".

The first compound preferably has a structure according to formula (I)

A1-Q-A2 (I)，

Wherein A is¹And A²Is a polar group independently selected from phosphine oxide groups and diazole groups, and Q is a direct bond or a spacer consisting of up to 100 covalently bound atoms preferably selected from C, H, B, Si, N, P, O, S, F, Cl, Br and I, which does not comprise a conjugated system of delocalized electrons.

The phosphine oxide group in the first compound is therefore preferably substituted by groups which either do not contain aromatic or heteroaromatic rings at all or only contain simple isolated aromatic or heteroaromatic rings which usually have from three to seven ring atoms and are separated from one another by structural moieties such As alkylene groups which do not contain delocalized electrons and thus hinder the conjugation of delocalized electrons between the attached aromatic or heteroaromatic rings.

More preferably, Q is an oligomeric methylene spacer of formula (Ib)

-(CH2)_x-(Ib)，

Wherein x is an integer equal to 1,2,3 or 4. Further preferably, the phosphine oxide polar group is selected from phosphine oxides substituted by two monovalent hydrocarbyl groups or one divalent hydrocarbylene group annulated to a phosphorus atom, and the total number of carbon atoms in the two hydrocarbyl groups or in the hydrocarbylene group is preferably from 2 to 60. In another preferred embodiment, two substantially covalent compounds are comprised in the semiconducting material, a first compound comprising a polar group selected from a phosphine oxide group and an oxadiazole group, wherein the first compound is free of a conjugated system of delocalized electrons or comprises a conjugated system of less than 10 delocalized electrons; and a second compound comprising a conjugated system of at least 10 delocalized electrons. More preferably, the second compound is free of polar groups selected from phosphine oxide groups and/or diazole groups.

More preferably, the conjugated system of delocalized electrons in the second compound comprises at least one aromatic ring following the H ü ckel rule.A more preferably, the conjugated system of delocalized electrons comprises a condensed aromatic skeleton containing at least 10 delocalized electrons, such as a naphthalene, anthracene, phenanthrene, pyrene, quinoline, indole or carbazole skeleton³Hybrid carbons, such as the carbon atom in the methylene group. Most preferably, the conjugated system comprising at least 10 delocalized electrons in the second compound is comprised in C₁₄-C₅₀Aromatic hydrocarbons or C₈-C₅₀The total number of carbon atoms in the heteroarene moiety also includes possible substituents. In the spirit of the present invention, the number, topology and spatial arrangement of substituents on the moiety comprising the delocalized electron-conjugated system is not critical to the function of the invention. Preferred heteroatoms in the heteroarene moiety are B, O, N and S. In the second compound, the core atom with the delocalized electron system comprised, as well as the polyvalent atoms such as C, Si, B (which preferably form peripheral substituents linked to said core atom), may be substituted by terminal atoms of elements which are generally monovalent in organic compounds and more preferably selected from H, F, Cl, Br and I. Further preferably, the second compound has a reduction potential value to tris (2-benzo [ d ] when measured by cyclic voltammetry under the same conditions]Thiazol-2-yl) phenoxyaluminum is more negative, preferably than 9,9',10,10' -tetraphenyl-2, 2 '-bianthracene or 2, 9-bis ([1,1' -biphenyl)]-4-yl) -4, 7-diphenyl-1, 10-phenanthroline is more negative, more preferably more negative than 2,4,7, 9-tetraphenyl-1, 10-phenanthroline, more preferably more negative than 9, 10-di (naphthalen-2-yl) -2-phenylanthracene, more preferably more negative than 2, 9-bis (2-methoxyphenyl) -4, 7-diphenyl-1, 10-phenanthroline, more preferably more negative than 9,9' -spirobis [ fluorene ]]-2, 7-diylbis (diphenylphosphine oxide) is less negative, even more preferably more negative than 4, 7-diphenyl-1, 10-phenanthroline, even more preferably more negative than 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene, most preferably more negative than pyrene and still preferably more negative than for [1,1' -binaphthyl]The values obtained for-2, 2' -diylbis (diphenylphosphine oxide) are more negative.

In a preferred embodiment, the electrically doped semiconducting material further comprises a metal salt additive consisting of at least one metal cation and at least one anion. Preferably, the metal cation is Li⁺Or Mg²⁺. Further preferably, the metal salt additive is selected from the group consisting of metal complexes comprising a 5-, 6-or 7-membered ring containing a nitrogen atom and an oxygen atom attached to the metal cation and complexes having a structure according to formula (II),

wherein A is¹Is C comprising at least one atom selected from O, S and N in the aromatic ring₆-C₃₀Arylene radicals or C₂-C₃₀A heteroarylene group, and A²And A³Each of which is independently selected from C containing at least one atom selected from O, S and N in the aromatic ring₆-C₃₀Aryl and C₂-C₃₀A heteroaryl group. Also preferably, the anion is selected from the group consisting of phenol anions substituted with phosphine oxide groups, 8-hydroxyquinoline anions and pyrazolyl borates. The metal salt additive preferably acts as a second n-type electrical dopant, more preferably it acts synergistically with the metal element present in elemental form and acts as a first n-type electrical dopant.

Preferably, said electropositive element in substantially elemental form is selected from Li, Na, K, Mg, Ca, Sr, Ba, Sm, Eu, Tm, Yb and Mn, more preferably from Li, Mg, Ca, Sr, Ba, Sm, Eu, Tm, Yb, most preferably from Li, Mg, Yb.

Further preferably, the molar ratio of the electropositive element to the first compound is below 0.5, preferably below 0.4, more preferably below 0.33, even more preferably below 0.25, even more preferably below 0.20, even more preferably below 0.17, most preferably below 0.15, still preferably below 0.13, still less preferably below 0.10.

It is furthermore preferred that the molar ratio of the electropositive element to the first compound is higher than 0.01, preferably higher than 0.02, more preferably higher than 0.03, even more preferably higher than 0.05, most preferably higher than 0.08.

The second object of the present invention is achieved by using as n-type electrical dopant in any of the electrically doped semiconductor materials defined above a metal selected from the group consisting of rare earth metals other than Sm, Eu and Yb or transition metals of the fourth period of the periodic table other than Mn and Zn.

The third object of the present invention is achieved by a method for manufacturing said semiconductor material, said method comprising the steps of co-evaporating and co-depositing under reduced pressure:

(i) an electropositive element selected from the group consisting of alkali metals, alkaline earth metals, rare earth metals, and transition metals of the fourth period of the periodic Table having a proton number of 22, 23, 24, 25, 26, 27, 28, 29, and

The first compound is a substantially covalent compound which contains no conjugated system of delocalized electrons, or contains a conjugated system of delocalized electrons with less than 10 conjugated delocalized electrons, and the value of the reduction potential of the organic compound is more negative than the value obtained for tris (2-benzo [ d ] thiazol-2-yl) phenoxyaluminum, preferably more negative than 9,9',10,10' -tetraphenyl-2, 2 '-bianthracene or 2, 9-bis ([1,1' -biphenyl ] -4-yl) -4, 7-diphenyl-1, 10-phenanthroline, more preferably more negative than 2,4,7, 9-tetraphenyl-1, 10-phenanthroline, even more preferably more negative than 9, if measured under the same conditions by cyclic voltammetry, 10-bis (naphthalen-2-yl) -2-phenylanthracene is more negative, even more preferably more negative than 2, 9-bis (2-methoxyphenyl) -4, 7-diphenyl-1, 10-phenanthroline, even more preferably more negative than 9,9' -spirobis [ fluorene ] -2, 7-diylbis (diphenylphosphine oxide), even more preferably more negative than 4, 7-diphenyl-1, 10-phenanthroline, even more preferably more negative than 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene, most preferably more negative than pyrene and still preferably more negative than the values obtained for [1,1' -binaphthyl ] -2,2' -diylbis (diphenylphosphine oxide),

wherein the electropositive element is deposited in its elemental or substantially elemental form. Preferably, the electropositive element is evaporated from its elemental or substantially elemental form, more preferably from a substantially air stable elemental or substantially elemental form. It is furthermore preferred that the pressure is below 10^-2Pa, more preferably less than 10^-3Pa, most preferably less than 10^-4Pa。

Preferably, the normal boiling point of the electropositive element is below 3000 ℃, more preferably below 2200 ℃, even more preferably below 1800 ℃, most preferably below 1500 ℃. At normal boiling point, it is understood to be the boiling point at atmospheric pressure (101.325 kPa).

It is to be understood that the term "substantially air-stable" refers to metals and their substantially elemental forms (e.g., alloys with other metals) that react with atmospheric gases and moisture at ambient conditions sufficiently slowly to avoid quality assurance problems when handling the forms at ambient conditions in industrial processes. More specifically, for the purposes of this application, if the weight is at least 1g and the air exposed surface is at least 1cm²A sample of this form of (a) can be held at a standard temperature of 25 ℃, a pressure of 101325 Pa and a relative humidity of 80% for at least one hour, preferably at least 4 hours, more preferably at least 24 hours and most preferably at least 240 hours, without showing a statistically significant weight increase (provided that the weighing accuracy is at least 0.1mg), then the metallic form will be determined to be substantially air stable.

Preferably, the electropositive element in substantially elemental form is selected from the group consisting of Li, Na, K, Mg, Ca, Sr, Ba, Sm, Eu, Tm, Yb and Mn, more preferably from the group consisting of Li, Mg, Ca, Sr, Ba, Sm, Eu, Tm, Yb, most preferably from the group consisting of Li, Mg, Yb. Further preferably, the electropositive element is evaporated from a substantially air stable elemental form or a substantially elemental form. Most preferably, the electropositive element is evaporated from a linear evaporation source. The first object of the present invention is also achieved by an electrically doped semiconductor material which can be prepared according to any of the above-mentioned methods of the present invention.

The fourth object of the invention is achieved by an electronic device comprising a cathode, an anode and a semiconductor material between the cathode and the anode, the semiconductor material comprising

The first compound is a substantially covalent compound which contains no conjugated system of delocalized electrons, or contains a conjugated system of delocalized electrons with less than 10 conjugated delocalized electrons, and the value of the reduction potential of the first compound is more negative than the value obtained for tris (2-benzo [ d ] thiazol-2-yl) phenoxyaluminum, preferably more negative than 9,9',10,10' -tetraphenyl-2, 2 '-bianthracene or 2, 9-bis ([1,1' -biphenyl ] -4-yl) -4, 7-diphenyl-1, 10-phenanthroline, more preferably more negative than 2,4,7, 9-tetraphenyl-1, 10-phenanthroline, even more preferably more negative than 9, if measured by cyclic voltammetry under the same conditions, 10-bis (naphthalen-2-yl) -2-phenylanthracene is more negative, even more preferably more negative than 2, 9-bis (2-methoxyphenyl) -4, 7-diphenyl-1, 10-phenanthroline, even more preferably more negative than 9,9' -spirobis [ fluorene ] -2, 7-diylbis (diphenylphosphine oxide), even more preferably more negative than 4, 7-diphenyl-1, 10-phenanthroline, even more preferably more negative than 1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene, most preferably more negative than pyrene and still preferably more negative than the values obtained for [1,1' -binaphthyl ] -2,2' -diylbis (diphenylphosphine oxide), or may be prepared by the above-mentioned method.

Preferred embodiments of the electronic device according to the invention comprise preferred embodiments of the inventive semiconductor material as described above. More preferably, a preferred embodiment of the electronic device according to the invention comprises the inventive semiconducting material prepared by any embodiment of the inventive method characterized above. Preferably, the device further comprises at least one light emitting layer between the anode and the cathode.

Preferably, the semiconductor material forms an electron transporting, electron injecting or charge injecting layer. More preferably, the electron transporting or electron injecting layer is adjacent to a layer composed of a compound having a reduction potential greater negative than that of the electron transporting host compound of the adjacent electron transporting or electron injecting layer when measured under the same conditions by cyclic voltammetry. In a preferred embodiment, the layer adjacent to the layer made of the semiconductor material of the invention is a light-emitting layer.

It is further preferable that the light emitting layer emits blue or white light. In a preferred embodiment, the light-emitting layer comprises at least one polymer. More preferably, the polymer is a blue light emitting polymer.

Further preferably, the electron transporting or electron injecting layer is thicker than 5nm, preferably thicker than 10nm, more preferably thicker than 15nm, even more preferably thicker than 20nm, most preferably thicker than 25nm, still preferably thicker than 50nm and still preferably thicker than 100 nm.

In a preferred embodiment, the electron transporting or electron injecting layer is adjacent to a cathode comprised of a semiconducting metal oxide. Preferably, the semiconducting metal oxide is indium tin oxide. Further preferably, the cathode is prepared by sputtering.

Yet another embodiment of the present invention is a tandem OLED stack comprising a metal doped pn junction comprising a semiconductor material comprising

Drawings

Fig. 1 shows a schematic diagram of a device into which the present invention may be incorporated.

Fig. 2 shows a schematic diagram of a device into which the present invention may be incorporated.

Fig. 3 shows absorbance curves for two n-type doped semiconductor materials; the circles represent the comparative matrix compound C10 doped with 10 wt.% of compound F1 (which forms a strong reducing group), and the triangles represent compound E10 doped with 5 wt.% of Mg.

Detailed Description

Device structure

Fig. 1 shows an anode (10), a stack of an organic semiconductor layer (11) comprising a light-emitting layer, an Electron Transport Layer (ETL) (12) and a cathode (13). As explained herein, other layers may be interposed between those depicted.

Fig. 2 shows a stack of an anode (20), a hole injection and transport layer (21), a hole transport layer (22) which may also integrate an electron blocking function, a light emitting layer (23), an ETL (24) and a cathode (25). As explained herein, other layers may be interposed between those depicted.

The word "device" includes organic light emitting diodes.

Material property-energy level

One method of determining the Ionization Potential (IP) is ultraviolet spectroscopy (UPS). The ionization potential of solid materials is typically measured; however, the IP in the gas phase can also be measured. Both values are distinguished by their solid state effect, e.g. the polarization energy of holes generated during the photoionization process. Typical values for the polarization energy are about 1eV, but large differences in value may also occur. IP is related to the onset of the photoemission spectrum (i.e., the energy of the weakest bound electron) in the region of high kinetic energy of the photoelectron. Electron Affinity (EA) can be determined using a method related to UPS, i.e., reflected electron spectroscopy (IPES). However, this method is not so commonSee. Electrochemical measurement in solution is to determine solid state oxidation (E)_{Oxidation by oxygen}) And reduction (E)_{Reduction of}) Alternative methods of electrical potential. For example, a suitable method is cyclic voltammetry. To avoid confusion, the claimed energy level is defined in terms of a comparison of reference compounds that have a well-defined redox potential in cyclic voltammetry when measured by a standardized procedure. Simple rules are generally used to convert redox potentials to electron affinity and ionization potential, respectively: IP (in eV) 4.8eV + E_{Oxidation by oxygen}(wherein E_{Oxidation by oxygen}To ferrocene

Ferrocene (Fc)⁺v/Fc) and EA (in eV) 4.8eV + E_{Reduction of}(E_{Reduction of}To relative to Fc⁺Volt values are given for/Fc) (see b.w.d' Andrade, org.electron. (organic electrons) 6,11-20(2005)), e is the element charge. Recalculating the conversion factor of the electrochemical potential is known in the case of other reference electrodes or other reference redox pairs (see a.j.bard, l.r.faulkner, "electrochemical methods: Fundamentals and Applications," Wiley, 2 nd edition 2000). Information on the effect of the solutions used can be found in n.g. connelly et al, chem.rev. (chemical review) 96,877 (1996). In general, the term "HOMO energy" E, respectively, is used even if not entirely accurate_(HOMO)And "LUMO energy" E_(LUMO)As synonyms for ionization energy and electron affinity (Koopmans theorem). It has to be taken into account that the ionization potential and the electron affinity, respectively, are usually reported in such a way that a larger value indicates a stronger binding of released or absorbed electrons. The energy scale of the leading molecular orbitals (HOMO, LUMO) is opposite to this. Thus, in a rough approximation, the following equation holds: IP ═ E_(HOMO)And EA ═ E_(LUMO)(zero energy is designated as vacuum).

For the selected reference compounds, the inventors obtained the relative Fc in Tetrahydrofuran (THF) solution by standardized cyclic voltammetry⁺The following reduction potential values of/Fc:

tris (2-benzo [ d ]]Thiazol-2-yl) phenoxyaluminum, CAS 1269508-14-6, -2.21V, B0;

9,9',10,10' -tetraphenyl-2, 2' -bianthracene (TPBA), CAS 172285-72-2, -2.28V, B1;

2, 9-bis ([1,1' -biphenyl)]-4-yl) -4, 7-diphenyl-1, 10-phenanthroline, CAS338734-83-1, -2.29V, B2;

2,4,7, 9-tetraphenyl-1, 10-phenanthroline, CAS 51786-73-3, -2.33V, B3;

9, 10-bis (naphthalen-2-yl) -2-Phenylanthracene (PADN), CAS 865435-20-7, -2.37V, B4;

2, 9-bis (2-methoxyphenyl) -4, 7-diphenyl-1, 10-phenanthroline, CAS553677-79-5, -2.40V, B5;

9,9' -spirobi [ fluorene]-2, 7-diylbis (diphenylphosphine oxide) (SPPO13), CAS 1234510-13-4, -2.41V, B6;

n2, N2, N2', N2', N7, N7, N7', N7' -octaphenyl-9, 9' -spirobi [ fluorene ]]-2,2',7,7' -tetraamine (spiro TAD), CAS 189363-47-1, -3.10V, B7;

triphenylene, CAS 217-59-4, -3.04V, B8;

n4, N4' -bis (naphthalen-1-yl) -N4, N4' -diphenyl- [1,1' -biphenyl]-4,4' -diamine (α -NPD), CAS 123847-85-8, -2.96V, B9;

4,4 '-bis (9H-carbazol-9-yl) -1,1' -biphenyl (CBP), CAS58328-31-7, -2.91V, B10;

bis (4- (9H-carbazol-9-yl) phenyl) (phenyl) phosphine oxide (BCPO), CAS1233407-28-7, -2.86, B11;

3- ([1,1' -Biphenyl)]-4-yl) -5- (4- (tert-butyl) phenyl) -4-phenyl-4H-1, 2, 4-Triazole (TAZ), -2.76V, B12;

pyrene, CAS 129-00-0, -2.64V, B13.

Examples of matrix compounds of state-of-the-art electrically doped semiconducting materials based on matrix compounds comprising a conjugated system of phosphine oxide groups and at least 10 delocalized electrons are

(9-phenyl-9H-carbazole-2, 7-diyl) bis (diphenylphosphine oxide) (PPO27), CAS 1299463-56-1, -2.51V, E1;

[1,1' -binaphthyl]-2,2' -diylbis (diphenyloxide)Phosphine Oxide) (BINAPO), CAS 86632-33-9, -2.69V, E2;

spiro [ dibenzo [ c, h ]]Xanthene-7, 9' -fluorene]-2', 7-diylbis (diphenylphosphine oxide), -2.36V, E3;

naphthalene-2, 6-diylbis (diphenylphosphine oxide), -2.41V, E4;

[1,1':4', 1' -terphenyl]-3, 5-diylbis (diphenylphosphine oxide), -2.58V, E5;

3-phenyl-3H-benzo [ b]Dinaphtho [2,1-d:1',2' -f]Phosphine-3-oxide, CAS597578-38-6, -2.62V, E6;

diphenyl (4- (9-phenyl-9H-carbazol-3-yl) phenylphosphine oxide, -2.81V, E7;

(9, 9-dihexyl-9H-fluorene-2, 7-diyl) bis (diphenylphosphine oxide), -2.52V, E8;

(3- (3, 11-Dimethoxydibenzo [ c, h ]]Acridin-7-yl) phenyl) diphenylphosphine oxide (described in WO2013/079217 a 1), -2.29V, E9;

(3- (2, 12-Dimethoxydibenzo [ c, h ]]Acridin-7-yl) phenyl) diphenylphosphine oxide (descriptionIn WO2013/079217 a 1), -2.24V, E10;

diphenyl (5- (pyrene-1-yl) pyridin-2-yl) phosphine oxide, described in WO2014/167020, -2.34V, E11;

diphenyl (4- (pyrene-1-yl) phenyl) phosphine oxide, described in PCT/EP2014/071659, -2.43V, E12;

(3- (anthracen-9-yl) phenyl) diphenylphosphine oxide, -2.78V, E13;

diphenyl- (3- (spiro [ fluorene-9, 9' -xanthene)]-2-yl) phenyl) phosphine oxide, -2.71V, E14;

diphenyl- (4- (spiro [ fluorene-9, 9' -xanthene)]-2-yl) phenyl) phosphine oxide, -2.65V, E15.

As a comparative compound, use

(4- (Dibenzo [ c, h)]Acridin-7-yl) phenyl) diphenylphosphine oxide (described in WO2011/154131 a 1), -2.20V, C1;

(6,6' - (1- (pyridin-2-yl) ethane-1, 1-diyl) bis (pyridine-6, 2-diyl)) bis (diphenylphosphine oxide), described in EP 2452946, -2.21V, C2;

2- (4- (9, 10-bis (naphthalen-2-yl) anthracen-2-yl) phenyl) -1-phenyl-1H-benzo [ d]Imidazole (LG-201), CAS 561064-11-7, -2.32V, C3;

7- (4' - (1-phenyl-1H-benzo [ d ]]Imidazol-2-yl- [1,1' -biphenyl]-4-yl) dibenzo [ c, h]Acridine (described in WO2011/154131 a 1), -2.24V, C4;

7- (4' - (1-phenyl-1H-benzo [ d ]]Imidazol-2-yl) phenyl) dibenzo [ c, h]Acridine (described in WO2011/154131 a 1), -2.22V, C5;

1,3, 5-tris (1-phenyl-1H-benzimidazol-2-yl) benzene (TPBI) CAS192198-85-9, -2.58V, C6;

4, 7-diphenyl-1, 10-phenanthroline (Bphen) CAS 1662-01-7, -2.47V, C7;

1, 3-bis [2- (2,2' -bipyridin-6-yl) -1,3,4-

Diazol-5-yl]Benzene (Bpy-OXD), -2.28V, C8;

(9, 10-bis (naphthalen-2-yl) anthracen-2-yl) diphenylphosphine oxide, CAS 1416242-45-9, -2.19V, C9;

4- (Naphthalen-1-yl) -2,7, 9-triphenylpyrido [2 ]3,2-h]Quinazolines according to EP 1971371, -2.18V, C10;

1, 3-bis (9-phenyl-1, 10-phenanthrolin-2-yl) benzene, CAS721969-84-4, -2.45V, C11.

Substrate

It may be flexible or rigid, transparent, opaque, reflective or translucent. If the light generated by the OLED is to be transmitted through the substrate (bottom emission), the substrate should be transparent or translucent. The substrate may be opaque if the light generated by the OLED is to be emitted in the opposite direction to the substrate (so-called top-emitting). The OLED may also be transparent. The substrate may be disposed adjacent to the cathode or the anode.

Electrode for electrochemical cell

The electrodes are anodes and cathodes, which must provide a certain amount of conductivity, preferably a conductor. The "first electrode" is preferably a cathode. At least one of the electrodes must be translucent or transparent to enable light to be transmitted to the exterior of the device. Typical electrodes are layers or stacks of layers comprising metal and/or transparent conductive oxides. Other possible electrodes are made of thin busbars (e.g. thin metal grids) wherein the space between the busbars is filled (coated) with a transparent material with a certain electrical conductivity, such as graphene, carbon nanotubes, doped organic semiconductors, etc.

In one embodiment, the anode is the electrode closest to the substrate, referred to as the non-inverted structure. In another mode, the cathode is the electrode closest to the substrate, referred to as the inverted structure.

Typical anode materials are ITO and Ag. Typical cathode materials are Mg: Ag (10% by volume of Mg), Ag, ITO, Al. Mixtures and multi-layer cathodes are also possible.

Preferably, the cathode comprises a metal selected from Ag, Al, Mg, Ba, Ca, Yb, In, Zn, Sn, Sm, Bi, Eu, Li, more preferably from Al, Mg, Ca, Ba and even more preferably from Al or Mg. Also preferred are cathodes comprising an alloy of Mg and Ag.

One advantage of the present invention is that it enables a wide selection of cathode materials. In addition to materials with low work functions, which are required in most cases for good performance of devices comprising the state-of-the-art n-doped ETL materials, other metals or conductive metal oxides can be used as cathode materials. It is particularly advantageous to use a cathode made of metallic silver, since pure silver offers the best reflectivity and therefore the best efficiency, especially for example in bottom-emitting devices built on a transparent substrate and having a transparent conductive oxide anode. Pure silver cathodes have not been built into devices with undoped ETL or ETL doped with metal salt additives because such devices exhibit high operating voltage and low efficiency due to poor electron injection.

It is also possible to form the cathode on the substrate beforehand (the device is then an inverted device), or to form the cathode in a non-inverted device by vacuum deposition of metal or by sputtering.

Hole Transport Layer (HTL)

The HTL is a layer comprising a large bandgap semiconductor responsible for transporting holes from the anode or holes from the CGL to the Light Emitting Layer (LEL). The HTL is included between the anode and the LEL or between the hole generating side of the CGL and the LEL. The HTL may be mixed with another material, such as a p-type dopant, in which case the HTL is said to be p-type doped. The HTL may include several layers that may have different compositions. The p-type doping of the HTL reduces its resistivity and avoids the corresponding power loss due to the high resistivity of the undoped semiconductor. The doped HTL can therefore also be used as an optical spacer layer, since it can be made very thick, up to 1000nm or more, without a significant increase in resistivity.

Suitable hole-transporting Hosts (HTMs) can be, for example, compounds from the diamine family, in which delocalized pi-electron systems conjugated to lone electron pairs on the nitrogen atom are provided at least between two nitrogen atoms of the diamine molecule. Examples are N4, N4' -bis (naphthalen-1-yl) -N4, N4' -diphenyl- [1,1' -biphenyl ] -4,4' -diamine (HTM1), N4, N4, N4', N4' -tetrakis ([1,1' -biphenyl ] -4-yl) - [1,1':4', 1' -terphenyl ] -4,4' -diamine (HTM 2). The synthesis of diamines is well described in the literature; many diamine HTMs are readily available commercially.

Hole Injection Layer (HIL)

The HIL is a layer that facilitates hole injection into the adjacent HTL from the anode or from the hole-generating side of the CGL. Typically, HIL is a very thin layer (<10 nm). The hole injection layer may be a pure layer of p-type dopant and may be about 1nm thick. When the HTL is doped, the HIL may not be necessary because the HTL already provides the implant function.

Luminous layer (LEL)

The light-emitting layer must comprise at least one light-emitting material and may optionally comprise additional layers. If the LEL comprises a mixture of two or more materials, the charge carrier injection may take place in different materials, for example in materials other than the emitter, or the charge carrier injection may also take place directly in the emitter. Many different energy transfer processes may occur within an LEL or an adjacent LEL, resulting in different types of light emission. For example, excitons may be formed in a host material and then transferred to an emitter material as singlet or triplet excitons, which may be a singlet or triplet emitter that then emits light. A mixture of different types of luminophores may be provided to increase the efficiency. White light can be achieved by using emissions from the emitter host and emitter dopant. In a preferred embodiment of the present invention, the light-emitting layer comprises at least one polymer.

Barriers may be used to improve the confinement of charge carriers in the LEL, these barriers being further explained in US 7,074,500B 2.

Electronic Transmission Layer (ETL)

The ETL is a layer comprising a large bandgap semiconductor responsible for transporting electrons from the cathode or from the CGL or EIL (see below) to the LEL. The ETL is contained between the cathode and the LEL or between the electron generating side of the CGL and the LEL. The ETL may be mixed with an n-type electrical dopant, in which case the ETL is said to be n-type doped. The ETL may include several layers that may have different compositions. The n-type electrical doping of the ETL reduces its resistivity and/or improves its ability to inject electrons into adjacent layers and avoids the corresponding power loss due to the high resistivity (and/or poor injection capability) of undoped semiconductors. The doped ETL can also be used as an optical spacer layer if the electrical doping used creates new charge carriers to the extent that the conductivity of the doped semiconductor material is greatly increased compared to the undoped ETM, since it can be made very thick, up to 1000nm or more, without a significant increase in the operating voltage of the device containing such doped ETL. A preferred mode of electrical doping that is predicted to generate new charge carriers is so-called redox doping. In the case of n-type doping, redox doping corresponds to the transfer of electrons from the dopant to the host molecule.

In the case of n-type electrical doping of a metal used as a dopant in its substantially elemental form, electron transfer from the metal atom to the host molecule is predicted to produce a metal cation and an anionic group of the host molecule. The currently predicted mechanism of charge transport in redox n-type doped semiconductors is the hopping of a single electron from an anionic group to an adjacent neutral host molecule.

However, with regard to redox electrical doping, it is difficult to understand all the properties of semiconductors doped with metallic n-type, in particular the semiconductor materials of the present invention. Thus, it is predicted that the semiconductor material of the present invention advantageously combines redox doping with the unknown advantageous effect of mixing ETM with metal atoms and/or clusters thereof. The semiconductor materials of the present invention are predicted to contain a significant portion of the added electropositive element in substantially elemental form. The term "substantially elemental" is understood to mean a form which is closer to the state of a free atom or a metal cluster than to the state of a metal cation or a positively charged metal cluster in terms of the electronic state and its energy.

Without being bound by theory, it is predicted that there is a significant difference between the prior art n-type doped organic semiconductor material and the n-type doped semiconductor material of the present invention. In the common organic ETM of the prior art (reduction potential approximately between-2.0 and-3.0V (vs. Fc)⁺Fc) and a conjugated system containing at least ten delocalized electrons) of a strong redox n-type dopant, such as an alkali metal or W₂(hpp)₄Predicting the generation of individual atoms or moieties of the dopant with external additionThe number of charge carriers is comparable to the number of photons, and there is indeed experience that: increasing the amount of such strong dopants in a conventional host beyond a particular level does not result in any substantial gain in the electrical properties of the doped material.

On the other hand, it is difficult to speculate what the n-type doping strength of the electropositive element will play in the matrix of the present invention which comprises mainly polar groups but only very little or no delocalized electron conjugated system.

It might still be predictable that in such a matrix, even for the most electropositive elements such as alkali metals, only a fraction of the added atoms of the electropositive element added as n-type dopants react with the matrix molecules via a redox mechanism to form the corresponding metal cations. Conversely, it is predicted that, even at high dilution, when the amount of the matrix is sufficiently higher than the amount of the added metallic element, most of the metallic element exists in a substantially elemental form. It is further predicted that if the metal element of the present invention is mixed with the matrix of the present invention in a comparable amount, most of the added metal element is present in the resulting doped semiconductor material in substantially elemental form. This hypothesis seems to provide a reasonable explanation for why the metallic elements of the present invention, even the weaker dopants, can be effectively used in a significantly wider range of ratios to the doping matrix than the stronger dopants of the prior art. Suitable contents of the metal element in the doped semiconductor material of the invention are generally in the range of 0.5 to 25 wt.%, preferably in the range of 1 to 20 wt.%, more preferably in the range of 2 to 15 wt.%, most preferably in the range of 3 to 10 wt.%.

The hole blocking layer and the electron blocking layer may be used as usual.

Other layers having different functions may be included and the device structure may be modified as known to those of ordinary skill in the art. For example, an Electron Injection Layer (EIL) made of a metal, metal complex or metal salt may be used between the cathode and the ETL.

Charge Generation Layer (CGL)

The OLED may comprise CGLs, which may be used as inverted contacts with electrodes, or as connection units in a stacked OLED. CGLs may have the most different configurations and names, examples being pn junctions, junction cells, tunnel junctions, etc. Preferred examples are pn-junctions as disclosed in US 2009/0045728a1, US 2010/0288362 a 1. Metal and or insulating layers may also be used.

Stacked OLED

When the OLED comprises two or more LELs separated by CGLs, the OLED is referred to as a stacked OLED, otherwise it is referred to as a single-cell OLED. A group of layers between two closest CGLs or between one electrode and the closest CGL is called an electroluminescent unit (ELU). Thus, the stacked OLED can be described as an anode/ELU₁/{CGL_X/ELU_1+X}_XA cathode, wherein x is a positive integer, and each CGL_XOr each ELU_1+XMay be equal or different. The CGL may also be formed from adjacent layers of two ELUs, as disclosed in US2009/0009072 a 1. Other stacked OLEDs are described in, for example, US 2009/0045728a1, US 2010/0288362 a1 and references therein.

Deposition of organic layers

Any organic semiconductor layer of the displays of the present invention may be deposited by known techniques such as Vacuum Thermal Evaporation (VTE), organic vapor deposition, laser induced thermal transfer, spin coating, doctor blading, slit dye coating, ink jet printing, and the like. A preferred method of preparing the OLED according to the invention is vacuum thermal evaporation. The polymeric material is preferably processed by coating techniques from a solution in a suitable solvent.

Preferably, the ETL is formed by evaporation. When an additional material is used in the ETL, the ETL is preferably formed by co-evaporation of an Electron Transport Matrix (ETM) and the additional material. The additional material may be homogeneously mixed in the ETL. In one mode of the invention, the additional material has a concentration variation in the ETL, wherein the concentration varies in a thickness direction of the stacked layers. It is also envisioned that the ETL is structured in sub-layers, wherein some, but not all, of these sub-layers contain the additional material.

The semiconductor materials of the present invention are predicted to contain a significant portion of the added electropositive element in substantially elemental form. Thus, the method of the invention requires evaporation of the electropositive element from its elemental or substantially elemental form. In this case, the term "substantially element" is to be understood as such form: in terms of electronic states and their energies and chemical bonds, they are closer to the form of elemental metal, free metal atoms or clusters of metal atoms than to the form of metal salts of covalent metal compounds or coordination compounds of metals. Generally, the metal vapor released from a metal alloy according to EP 1648042B 1 or WO2007/109815 is understood to be the evaporation from the substantially elemental form of the evaporating metal.

Electric doping

The most reliable and at the same time efficient OLEDs are OLEDs comprising an electrically doped layer. In general, electrical doping means an improvement in the electrical properties, in particular the conductivity and/or the implantation ability, of the doped layer compared to a purely charge transporting host without dopant. In a narrow sense, which is often referred to as redox doping or charge transfer doping, the hole transport layer is doped with a suitable acceptor material (p-type doping) or the electron transport layer is doped with a suitable donor material (n-type doping), respectively. By redox doping, the density (and thus the conductivity) of charge carriers in the organic solid can be substantially increased. In other words, redox doping increases the charge carrier density of the semiconductor matrix compared to the charge carrier density of an undoped matrix. The use of doped charge carrier transport layers in organic light emitting diodes (p-type doping of the hole transport layer by mixing with receptor-like molecules, n-type doping of the electron transport layer by mixing with donor-like molecules) is for example described in US 2008/203406 and US 5,093,698.

US2008227979 discloses in detail charge transfer doping of organic transport materials with inorganic and organic dopants. Basically, efficient electron transfer from the dopant to the host raises the fermi level of the host. For efficient transfer in the case of p-type doping, the LUMO level of the dopant is preferably more negative than the HOMO level of the host, or at least not more than slightly positive than the HOMO level of the host, preferably not more than 0.5eV positive. For the case of n-type doping, the HOMO level of the dopant is preferably more positive than the LUMO level of the host, or at least not more negative than slightly, preferably not more than 0.5eV lower than the LUMO level of the host. It is also desirable that the energy level difference of the energy transfer from the dopant to the host is less than +0.3 eV.

Typical examples of known redox-doped hole transport materials are copper phthalocyanine (CuPc) doped with tetrafluoro-tetracyanoquinodimethane (F4TCNQ) with a LUMO level of about-5.2 eV (HOMO level of about-5.2 eV), zinc phthalocyanine (ZnPc) doped with F4TCNQ (HOMO ═ 5.2eV), α -NPD (N, N '-bis (naphthalen-1-yl) -N, N' -bis (phenyl) -benzidine) doped with F4TCNQ, α -NPD doped with 2,2'- (perfluoronaphthalene-2, 6-diylidene) dipropylenedinitrile (PD1), α -NPD doped with 2,2',2 "- (cyclopropane-1, 2, 3-triylidene) tris (2- (p-cyanotetrafluorophenyl) acetonitrile) (PD 2. all p-type dopings in the device examples of the present application are carried out with 3 mol% PD 2.

Typical examples of known redox-doped electron transport materials are: fullerene C60 doped with Acridine Orange Base (AOB); perylene-3, 4,9, 10-tetracarboxylic-3, 4,9, 10-dianhydride (PTCDA) doped with colorless crystal violet; doped with tetrakis (1,3,4,6,7, 8-hexahydro-2H-pyrimido [1, 2-a)]Pyrimido) ditungsten (II) (W)₂(hpp)₄) 2, 9-bis (phenanthren-9-yl) -4, 7-diphenyl-1, 10-phenanthroline; naphthalene tetracarboxylic dianhydride (NTCDA) doped with 3, 6-bis (dimethylamino) -acridine; NTCDA doped with bis (ethylenedithiol) tetrathiafulvalene (BEDT-TTF).

In addition to redox dopants, certain metal salts may optionally be used for n-type electrical doping, resulting in a reduced operating voltage for a device comprising a doped layer compared to the same device without the metal salt. The true mechanism by which these metal salts (sometimes referred to as "electrical doping additives") contribute to the reduction of voltage in electronic devices is not known. It is believed that they change the barrier at the interface between adjacent layers rather than the conductivity of the doped layers, since they only achieve a positive effect on the operating voltage when the layers doped with these additives are very thin. Typically, the electrically undoped or additive doped layer is thinner than 50nm, preferably thinner than 40nm, more preferably thinner than 30nm, even more preferably thinner than 20nm, most preferably thinner than 15 nm. If the manufacturing process is sufficiently accurate, the additive doping layer can advantageously be made thinner than 10nm or even thinner than 5 nm.

Typical representatives of metal salts effective as second electrical dopants in the present invention are salts comprising metal cations with one or two elementary charges. Advantageously, alkali metal salts or alkaline earth metal salts are used. The anion of the salt is preferably one that provides sufficient volatility to the salt to enable it to be deposited under high vacuum conditions, particularly within a temperature and pressure range commensurate with the temperature and pressure range suitable for deposition of the electron transporting substrate.

An example of such an anion is the 8-hydroxyquinoline anion. A metal salt thereof, for example, lithium 8-hydroxyquinoline (LiQ) represented by the formula D1

Are well known as electrical doping additives.

Another class of metal salts that can be used as electrical dopants in the electron transport matrix of the present invention are the compounds having the general formula (II) disclosed in application PCT/EP2012/074127(WO2013/079678),

wherein A is¹Is C₆-C₂₀Arylene radical and A²-A³Each of which is independently selected from C₆-C₂₀Aryl, wherein the aryl or arylene group may be unsubstituted or substituted with a group comprising C and H or with another LiO group, provided that a given number of C in the aryl or arylene group also includes all substituents present on the group. It is to be understood that the term substituted or unsubstituted arylene represents a divalent radical derived from a substituted or unsubstituted arene, wherein two adjacent moieties (in formula (I), the OLi group and the diarylphosphine oxide group) are directly attached to the aromatic ring of the arylene group. In the examples of the present application, thisThe dopant-like is represented by compound D2

Wherein Ph is phenyl.

Another class of metal salts that can be used as electrical dopants in the electron-transporting matrix of the invention are the compounds of general formula (III) disclosed in application PCT/EP2012/074125(WO2013/079676)

Wherein M is a metal ion, A⁴To A⁷Each of which is independently selected from H, substituted or unsubstituted C₆-C₂₀Aryl and substituted or unsubstituted C₂-C₂₀Heteroaryl, and n is the valence of the metal ion. In the examples of the present application, such dopants are represented by compound D3

Advantageous effects of the invention

The advantageous effects of the electrically doped semiconductor material of the present invention are shown in comparison to a comparative device comprising not the combination of electron transporting host and dopant of the present invention, but other combinations of host and dopant known in the art. The devices used are described in detail in the examples.

In the first screening stage, 32 host compounds were tested in the device of example 1, with 5 wt% Mg as dopant. Comprises a phosphorus oxide matrix and is stabilized against Fc⁺The electron transport matrix, whose reduction potential of/Fc represents a LUMO energy level (measured by cyclic voltammetry in THF) higher than that of compound B0 (-2.21V under the standardised conditions used), outperformed C1 and C2 in terms of operating voltage and/or quantum efficiency of the device, and was significantly better than the matrix lacking phosphine oxide groups, independently of its LUMO energy level. For a plurality of themThese observations are also confirmed by its divalent metals, i.e., Ca, Sr, Ba, Sm, and Yb.

The results are summarized in Table 1, in which the relative changes in voltage and efficiency (both at a current density of 10 mA/cm) are calculated with respect to the C2/Mg system of the prior art considered as reference²The following measurements). The total score is calculated by subtracting the relative voltage change from the relative efficiency change.

TABLE 1

In the second stage of the study, two different ETL thicknesses of 40nm (U) were utilized in the device 2 in the matrices E1, E2 and C1₁And U₃) And 80nm (U)₂And U₄) And using two different doping concentrations of 5 wt.% (U)₁And U₂) And 25 wt.% (U)₃And U₄) All at a current density of 10mA/cm²Next, various metals were tested.

The results summarized in table 2 lead to the following preliminary conclusions: metals capable of forming stable compounds in oxidation state II are particularly suitable for n-type doping in a phosphorus oxide matrix, but they are significantly less reactive and have significantly higher air stability than the least reactive alkali metals (Li). From the divalent metals tested, only zinc with a very high sum of the first and second ionization potentials cannot serve as an n-type dopant, whereas aluminum with typical oxidation state III provides a reasonably low operating voltage only when present in the doped ETL at a high concentration (25 wt%), which results in an ETL with impractically high light absorption. In table 2 only the transmission with respect to the 25 wt.% doping concentration is reported, which is designated "OD", representing the "optical density" (OD for a layer thickness of 40 nm)₃And OD at 80nm for the layer thickness₄) Because the measured values for the lower doping concentration are less reproducible.

Generally trivalent bismuth does not function as an n-dopant at all, although its ionization potential is not very different from manganese, which for example shows a rather surprisingly good doping effect at least in E1.

Difference U₁-U₂And U₃-U₄Can be given a doped material with a high conductivity (the voltage of the device depends only weakly on the thickness of the doped layer).

TABLE 2

It has been observed that in hosts with deep LUMO, such as C1, although many doped semiconductor materials based on C1 have good electrical conductivity, their operating voltages are often surprisingly high compared to the operating voltages of devices containing hosts with LUMO levels within the range according to the present invention. It is clear that good electrical conductivity of a semiconductor material is not a sufficient condition for a low operating voltage of a device comprising the semiconductor material. Based on this finding, it is predicted that the doped semiconductor material according to the present invention is capable of efficiently injecting charges from the doped layer into adjacent layers, in addition to a reasonable conductivity.

In a third study phase, the observed effect was demonstrated in the OLED of example 3, which contains an alternative emitter system, and the other embodiments of the invention described in examples 4-7 were carried out. The results of the realizations summarized in table 3 demonstrate the surprising superiority of phosphine oxide ETL matrices with higher LUMO levels (close to vacuum level), although these matrices should be more difficult to dope with the relatively less reducing metals used in the present invention than the phosphine oxide matrices of the prior art (e.g., C1) which are considered to be dopable with Mg due to their deeper LUMO (further away from vacuum level) and specific structure comprising metal complexing units.

This series of experiments demonstrated that matrix compounds with rather high LUMO energy levels, such as E1 and E2, performed better than other phosphine oxide matrix compounds, also in the presence of other luminophores, and much better than matrices lacking phosphine oxide groups.

These results show that even substantially air-stable metals which in addition have other technically advantageous features, such as good evaporability, can provide electrically doped semiconductor materials and devices with properties comparable to or even better than those obtainable in the prior art, if combined with phosphine oxide matrices having a sufficiently high LUMO energy level.

TABLE 3

*ABH-112/NUBD-369+ABH-036/NRD129(Sun Fine Chemicals)

Finally, the focus point returns to the starting point. The remaining objective was to make the redox potential of comparative compound C2 significantly more negative and to test whether the corresponding LUMO energy level closer to zero on the absolute energy scale has a similar positive effect as the above-described matrix compound in phosphine oxide compounds comprising a small conjugated system with less than 10 delocalized electrons. This task is relatively easy to accomplish with the commercially available compounds A1-A4. All of these compounds have redox potentials that are difficult to measure by standard procedures using THF as a solvent because their values are more negative for compound B7.

Methylenebis (diphenylphosphine oxide), A1

Ethane-1, 2-diylbis (diphenylphosphine oxide), A2

Propane-1, 3-diylbis (diphenylphosphine oxide), A3

Butane-1, 4-diylbis (diphenylphosphine oxide), A4.

In contrast to these expectations, it was surprisingly found that even if the compounds have delocalized electron conjugated systems as small as the hexaelectron H ü ckel system in isolated aromatic or heteroaromatic rings, sufficiently strong dopants can provide good quality semiconductor materials, provided that said compounds still comprise polar groups selected from phosphine oxides and diazoles.

Examples

Auxiliary material

4,4',5,5' -tetracyclohexyl-1, 1',2,2',3,3 '-hexamethyl-2, 2',3,3 '-tetrahydro-1H, 1' H-biimidazole, CAS 1253941-73-9, F1;

2, 7-bis (naphthalen-2-yl) spiro [ fluorene-9, 9' -xanthene]LUMO (CV vs Fc)⁺/Fc)-2.63V，WO2013/149958，F2；

N3, N3 '-bis ([1,1' -biphenyl)]-4-yl) -N3, N3 '-ditrimethylphenyl- [1,1' -biphenyl]3,3' -diamine, WO2014/060526, F3;

biphenyl-4-yl (9, 9-diphenyl-9H-fluoren-2-yl) - [4- (9-phenyl-9H-carbazol-3-yl) phenyl]-amines, CAS 1242056-42-3, F4;

1- (4- (10- (([1,1' -biphenyl))]-4-yl) anthracen-9-yl) phenyl) -2-ethyl-1H-benzo [ d]Imidazole, CAS 1254961-38-0, F5;

2, 7-bis ([1,1' -biphenyl)]-4-yl) spiro [ fluorene-9, 9' -xanthene]LUMO (CV vs Fc)⁺/Fc)-2.63V，WO2013/149958，CAS 1466444-48-3，F6。

Auxiliary programs

Cyclic voltammetry

The redox potentials given for the specific compounds were measured under an argon atmosphere in an anhydrous THF solution of argon-degassed 0.1M test substance, using a 0.1M tetrabutylammonium hexafluorophosphate supporting electrolyte between platinum working electrodes and using a Ag/AgCl standard electrode consisting of a silver wire covered with silver chloride and immersed directly into the measurement solution, at a scan rate of 100 mV/s. The first operation is performed within the widest potential range set on the working electrode, and then the range is adjusted in the subsequent operation as appropriate. The last three runs were carried out with addition of ferrocene (0.1M concentration) as standard. The average of the potentials of the cathodic and anodic peaks corresponding to the compound studied, after subtraction of the standard Fc⁺The values are finally obtained after averaging the cathode and anode potentials observed for the/Fc redox couple. All the phosphine oxide compounds studied as well as the reported comparative compounds show well-defined reversible electrochemical behavior.

Synthetic examples

The synthesis of phosphine oxide ETL matrix compounds is well described in numerous publications, except in the literature where typical multistep procedures for the use of these compounds are cited and described at the specific compounds listed above, compound E6 is prepared very specifically by anionic rearrangement of compound E2, according to bull. chem. soc. jpn. (published by the japanese society of chemistry), 76,1233-1244 (2003).

For the unpublished compounds, typical procedures were used, as exemplified in particular below for compounds E5 and E8. All synthetic steps were performed under an argon atmosphere. Commercial material was used without additional purification. The solvent was dried by suitable means and degassed by saturation with argon.

Synthesis example 1

[1,1':4',1 "-terphenyl ] -3, 5-diylbis-diphenylphosphine oxide (comparative compound E5)

Step 1: 3, 5-dibromo-1, 1':4', 1' -terphenyl

All components (10.00g (1.0 equivalent, 50.50 mmol) of [1,1' -biphenyl]-4-yl-boronic acid, 23.85g (1.5 eq, 75.75 mmol) 1,3, 5-tribromobenzene, 1.17g (2.0 mol%, 1.01 mmol) tetrakis (triphenylphosphine) palladium (0), 10.70g (2 eq, 101 mmol) sodium carbonate in 50mL water, 100mL ethanol and 310mL toluene) were mixed together and stirred at reflux for 21 hours. The reaction mixture was cooled to room temperature and diluted with 200mL of toluene (three layers appeared). The aqueous layer was extracted with 100mL of toluene and the combined organic layers were washed with 200mL of water, dried and evaporated to dryness. By column chromatography (SiO)₂Hexane/DCM 4:1v/v) purify the crude material. The combined fractions were evaporated, suspended in hexane and filtered to give 9.4g of a white shiny solid (48% yield, 99.79% HPLC purity).

Step 2: [1,1':4', 1' -terphenyl ] -3, 5-diylbis-diphenylphosphine oxide

All components (5.00g (1.0 equivalent, 12.9 mmol), 3, 5-dibromo-1, 1':4',1 "-terphenyl from previous step, 12.0g (5.0 equivalent, 64.4 mmol) diphenylphosphine, 114mg (5 mol%, 6.44X 10 mmol)^-4Moles) palladium (II) chloride, 3.79g (3.0 equiv., 38.6 mmol) potassium acetate and 100mL N, N-dimethylformamide) were mixed together and stirred at reflux for 21 hours. The reaction mixture was then cooled to room temperature; water (100mL) was added and the mixture was stirred for 30 minutes, then filtered. The solid was redissolved in DCM (100mL) and H was added dropwise₂O₂(30 wt% aqueous solution), and the solution was stirred at room temperature overnight. The organic layer was then decanted, washed twice with water (100mL) and MgSO₄Dried and evaporated to dryness. The resulting oil was triturated in hot MeOH (100mL), which induced solid formation. After filtration while hot, the resulting solid was washed with MeOH and dried to give 9.7g of crude product. The crude material was redissolved in DCM and chromatographed on a short silica column eluting with ethyl acetate. After evaporation of the eluate to dryness, the resulting solid was triturated in hot MeOH (100mL) followed by hot EtOHTriturated in ethyl acetate (50 mL). After drying, the desired compound was obtained in a yield of 70% (5.71 g). Finally, vacuum sublimation was used to purify the product.

The pure subliming compound was amorphous, had no detectable melting peak on the DSC curve, started a glass transition at 86 ℃, and started to decompose at 490 ℃.

Synthesis example 2

(9, 9-dihexyl-9H-fluorene-2, 7-diyl) bis-diphenylphosphine oxide (comparative compound E8)

2, 7-dibromo-9, 9-dihexylfluorene (5.00g, 1.0 equivalent, 10.2 mmol) was placed in a flask and degassed with argon. Anhydrous THF (70mL) was then added and the mixture was cooled to-78 ℃. 9.7mL (2.5M solution in hexanes, 2.4 equivalents, 24.4 mmol) of n-butyllithium were then added dropwise; the resulting solution was stirred at-78 ℃ for 1 hour and then gradually warmed to-50 ℃. After the slow addition of pure chlorodiphenylphosphine (4.0mL, 2.2 equivalents, 22.4 mmol), the mixture was stirred overnight until room temperature. MeOH (20mL) was added to quench the reaction, and the solution was evaporated to dryness. The solid was redissolved in DCM (50mL) and H was added dropwise₂O₂(30 wt% aqueous solution, 15mL) and the mixture was left under stirring. After 24 hours, the organic phase is separated and subsequently washed with water and brine, over MgSO₄Dried and evaporated to dryness. Purification by chromatography (silica, gradient elution from hexanes/EtOAc 1:1v/v to pure EtOAc) afforded the desired compound in 34% yield (2.51 g). The material was then further purified by vacuum sublimation.

The pure subliming compound is amorphous, has no detectable melting peak on the DSC curve, and decomposes at 485 ℃.

Device embodiments

Comparative example 1 (blue OLED)

A first blue light emitting device was fabricated by depositing a 40nm HTM2 layer doped with PD2 (97:3 wt% host to dopant weight ratio) on an ITO glass substrate followed by a 90nm undoped HTM1 layer. Subsequently, a blue fluorescent light-emitting layer doped with ABH113(Sun Fine Chemicals) (97:3 wt%) of NUBD370(Sun Fine Chemicals) was deposited at a thickness of 20 nm. A layer of 36nm of the test compound is deposited on the light-emitting layer as ETL together with the required amount of the metal element (typically, with 5 wt% Mg). Subsequently, an aluminum layer with a thickness of 100nm was deposited as a cathode.

At a current density of 10mA/cm²The voltages and quantum efficiencies observed below are reported in table 1.

Comparative example 2 (organic diode)

Similar devices were fabricated as in example 1, except that the emitter was omitted and each combination host-dopant was tested at two different thicknesses of ETL (40 and 80nm) and two different dopant concentrations (5 and 25 wt%). At a current density of 10mA/cm²The voltages observed below and the light absorption of the device measured anywhere are reported in table 2.

Comparative example 3 (blue or white OLED)

Similar devices were fabricated as in example 1, except that semiconductor materials of various compositions were combined with various emitter systems in the ETL. The results were evaluated similarly to example 1 and are summarized in table 3.

Comparative example 4 (blue OLED)

In the device of example 1, the Al cathode was replaced with a sputtered Indium Tin Oxide (ITO) cathode in combination with Mg or Ba doped ETL. The results show that ETLs based on divalent metal doped phosphine oxide matrices with redox potential in the range of-2.24V to-2.81V versus Fc +/Fc are also suitable for top emitting OLEDs with cathodes made of transparent semiconducting oxides.

Comparative example 5 (transparent OLED)

A polymer light emitting layer comprising a blue light emitting polymer (provided by Cambridge display technology) was successfully tested as in example 1 in a transparent device with a p-side (substrate with ITO anode, HTL, EBL) and sputtered with a 100nm thick ITO cathode as in example 4. The results reported in table 4 (along with the n-side composition of the device, which is in all casesThe Below both comprising a 20nm thick HBL consisting of F2 and an ETL1 consisting of E2 and D3 in a weight ratio of 7:3 and having the thicknesses given in the tables) show that ETL based on a phosphine oxide compound doped with a divalent metal is about-2.8V even for a very high LUMO level (according to which relative to Fc⁺Redox potential/Fc reference) polymer LEL is also suitable. Without the metal-doped ETL, the device has (at a current density of 10 mA/cm), even when an EIL made of pure metal is deposited under the ITO electrode²Lower) very high voltage.

TABLE 4

Comparative example 6 (Metal deposition Using Linear Evaporation Source)

The evaporation behaviour of Mg in a linear evaporation source was tested. It has been shown that Mg can be deposited from a linear source at rates up to 1nm/s without sputtering, while a point evaporation source sprays Mg particles significantly at the same deposition rate.

Comparative example 7 (Metal + Metal salt electro-doping in the same ETL)

Comprising a matrix and LiQ + Mg or W₂(hpp)₄The mixed ETL combined with the two-component doping system shows the superiority of the salt + metal combination.

Comparative example 8 (tandem white OLED)

On an ITO substrate, the following layers were deposited by vacuum thermal evaporation:

a 10nm thick HTL consisting of 92 wt% of auxiliary material F4 doped with 8 wt% PD2, a 135nm thick layer of pure F4, a 25nm thick blue light-emitting layer ABH113(Sun Fine Chemicals) (97:3 wt%) doped with NUBD370(Sun Fine Chemicals), a 20nm thick layer ABH036(Sun Fine Chemicals), a 10nm thick CGL consisting of 95 wt% of compound E12 doped with 5 wt% Mg, a 10nm thick HTL consisting of 90 wt% of auxiliary material F4 doped with 10 wt% PD2, a 30nm thick layer of pure F4, a 15nm thick layer of pure F3, a 30nm thick proprietary yellow light-emitting layer, a 35nm thick layer of auxiliary material F5, a 1nm thick layer of LiF and an aluminum cathode. The EQE of a diode operating at 6.81V was 24.4%.

Comparative example 9 (tandem white OLED)

Example 8 was repeated, using Yb instead of Mg in CGL. The EQE of a diode operating at 6.80V is 23.9%.

Comparative example 10 (tandem white OLED)

Example 9 was repeated, replacing E12 in CGL with compound E6. The EQE of a diode operating at 6.71V was 23.7%.

Inventive example and comparative example 11 (Charge injection into Adjacent or Mixed high LUMO ETM in blue OLED)

Example 1 was repeated with the following modifications:

on an ITO substrate, a 10nm thick HTL consisting of 92 wt% of an auxiliary material F4 doped with 8 wt% PD2 was deposited by VTE followed by a 130nm thick layer of pure F4. Over the same light emitting layer as in example 1, 31nm thick HBL of F6 was deposited and subsequently over it a doped ETL according to table 5 was deposited, followed by an aluminum cathode. All deposition steps are below 10^-2Pa, by VTE.

TABLE 5

Experiments convincingly show that compounds a2 and a4 and their mixtures with ETMs without polar groups provide electron injection as good as more complex and significantly more expensive ETMs specifically designed to combine the presence of polar groups and conjugated systems with at least 10 delocalized electrons in one molecule. The model device also mimics the properties of a device comprising a light emitting layer made of a light emitting polymer due to the high negative reduction potential and low polarity of the F6 layer.

Inventive example and comparative example 12 (Charge injection into Adjacent or Mixed high LUMO ETM in blue OLED)

Example 11 was repeated, wherein F6 in HBL was replaced by B10. The composition of the ETL and the results are shown in table 6.

TABLE 6

The results show that the semiconductor material of the present invention also allows efficient injection of electrons into the CBP layer with a redox potential more negative than the HBL matrix of the previous example.

Inventive example and comparative example 13 (applicability of inventive semiconductor material in very thick ETL)

Example 11 was repeated, wherein the thickness of the ETL was 150 nm. The results are shown in Table 7.

TABLE 7

Comparison with table 5 shows that, despite the increase in thickness of the ETL by more than four times, the devices utilizing the inventive materials comprising compounds a2 and a4 in the ETL actually exhibit the same operating voltage as the device of example 11. The excellent electron injection and the resulting high conductivity in the semiconductor material of the invention thus enable the size of the optical cavity in an electronic device comprising a light emitting layer, e.g. a light emitting polymer, having a strongly negative redox potential to be adjusted.

The features disclosed in the foregoing description, in the claims and in the accompanying drawings may, both separately and in any combination thereof, be material for realizing the invention in diverse forms thereof. Table 8 summarizes the reference values of the physicochemical properties (first and second ionization potentials, normal boiling point, standard redox potential) relevant to the present invention.

TABLE 8

¹Yiming Zhang, Julian R.G. Evans, Shoufeng Yang, Corrected Values for Boiling Points and Enthalpies of Vaporization of Elements in handbook from Journal of Chemical&Engineering Data (chemistry)And engineering journal) 56,2011, page 328-337; the values correspond to the values given in the article for the individual elements in the current german version wikipedia.

²http://en.wikipedia.org/wiki/Ionization_energies_of_the_elements_％28data_page％29

Abbreviations used

CGL Charge Generation layer

CV cyclic voltammetry

DCM dichloromethane

DSC differential scanning calorimetry

EIL electron injection layer

External quantum efficiency of EQE electroluminescence

ETL Electron transport layer

ETM electron transport matrices

EtOAc ethyl acetate

Fc⁺/FcFerrocene

Ferrocene reference system

h hours

HIL hole injection layer

Highest occupied molecular orbital of HOMO

HTL hole transport layer

HTM hole transport matrix

ITO indium tin oxide

LUMO lowest unoccupied molecular orbital

LEL luminescent layer

LiQ 8-hydroxyquinoline lithium

MeOH methanol

Mole% mole percent

OLED organic light emitting diode

QA quality assurance

RT Room temperature

THF tetrahydrofuran

UV ultraviolet (light)

Volume% percent by volume

v/v volume/volume (ratio)

VTE vacuum thermal evaporation

Weight% wt. -% (mass)% of

Claims

1. A semiconductor material comprising

The first compound is a substantially covalent compound that contains no conjugated system of delocalized electrons, or a conjugated system of delocalized electrons with less than 10 conjugated delocalized electrons, and has a reduction potential value that is more negative than the value obtained for tris (2-benzo [ d ] thiazol-2-yl) phenoxyaluminum if measured by cyclic voltammetry under the same conditions.

2. The semiconducting material of claim 1, further comprising at least one second compound, wherein the second compound is a substantially covalent compound comprising a conjugated system of at least ten delocalized electrons.

3. The semiconducting material of claim 2, wherein the second compound has a reduction potential value that is more negative than tris (2-benzo [ d ] thiazol-2-yl) phenoxyaluminum when measured by cyclic voltammetry under the same conditions.

4. Semiconducting material according to any of claims 1 to 3, wherein at least one compound contains at least one aromatic or heteroaromatic ring.

5. Semiconducting material according to claim 4, wherein at least one compound comprises at least two aromatic or heteroaromatic rings connected or fused by covalent bonds.

6. The semiconductor material of any one of claims 1 to 3, wherein the electropositive element is selected from Li, Na, K, Mg, Ca, Sr, Ba, Sm, Eu, Tm, Yb and Mn.

7. The semiconductor material of any one of claims 1 to 3, wherein a molar ratio of the electropositive element to the first compound is below 0.5.

8. The semiconductor material of any one of claims 1 to 3, wherein the molar ratio of the electropositive element to the first compound is higher than 0.01.

9. Semiconducting material according to any of claims 1 to 3, wherein the first compound has a structure according to formula (I)

A¹-Q-A²(I)

10. The semiconducting material of claim 9, where Q is an oligomethylene spacer of formula (II)

-(CH₂)_x- (II)，

Wherein x is an integer equal to 1,2,3 or 4.

11. Semiconducting material according to any of claims 1-3, wherein the phosphine oxide polar group is selected from phosphine oxides substituted by two monovalent hydrocarbyl groups or one divalent hydrocarbylene group annulated to a phosphorus atom, and the total number of carbon atoms in the hydrocarbyl groups or in the hydrocarbylene groups is 2-60.

12. Semiconducting material according to any of claims 1-3, wherein the diazole polar group is an imidazole group.

13. Semiconducting material according to any of claims 2 to 3, wherein the conjugated system of at least 10 delocalized electrons is comprised in C₁₄-C₅₀Aromatic hydrocarbons or C₈-C₅₀In the heteroarene moiety.

14. Semiconducting material according to any of claims 1 to 3, further comprising a metal salt additive consisting of at least one metal cation and at least one anion.

15. The semiconducting material of claim 14, wherein the metal cation is Li⁺Or Mg²⁺。

16. The semiconducting material of claim 14, wherein the metal salt additive is selected from the group consisting of a metal complex comprising a 5-, 6-, or 7-membered ring containing a nitrogen atom and an oxygen atom attached to the metal cation and a complex having a structure according to formula (II),

wherein A is¹Is C comprising at least one atom selected from O, S and N in the aromatic ring₆-C₃₀Arylene radicals or C₂-C₃₀A heteroarylene group, and A²And A³Each of which is independently selected from C containing at least one atom selected from O, S and N in the aromatic ring₆-C₃₀Aryl and C₂-C₃₀A heteroaryl group.

17. Semiconducting material according to claim 14, wherein the anion is selected from the group consisting of phenol anions substituted with phosphine oxide groups, 8-hydroxyquinoline anions and pyrazolyl borates.

18. A method of manufacturing a semiconductor material according to any one of claims 1 to 17, comprising the steps of co-evaporating and co-depositing under reduced pressure:

Said first compound being a substantially covalent compound containing no conjugated system of delocalized electrons, or containing a conjugated system of delocalized electrons having less than 10 conjugated delocalized electrons, and having a reduction potential value that is more negative than the value obtained for tris (2-benzo [ d ] thiazol-2-yl) phenoxyaluminum if measured by cyclic voltammetry under the same conditions,

wherein the electropositive element is deposited in elemental or substantially elemental form.

19. The method of claim 18, wherein the electropositive element is evaporated from its elemental or substantially elemental form.

20. The method of claim 18 or 19, wherein the electropositive element is selected from Li, Na, K, Mg, Ca, Sr, Ba, Sm, Eu, Tm, Yb, and Mn.

21. An electronic device comprising a cathode, an anode and the semiconducting material of any of claims 1-17 between the cathode and the anode.

22. Electronic device according to claim 21, wherein the semiconductor material according to any one of claims 1 to 17 is comprised in an electron transporting, electron injecting or charge generating layer.

23. The electronic device of claim 22, wherein the electron transporting or electron injecting layer is thicker than 5 nm.

24. The electronic device of any one of claims 21 to 23, further comprising at least one light emitting layer between the anode and the cathode.

25. An electronic device according to claim 24 wherein the light emitting layer consists of a compound having a reduction potential that is more negative than the second compound defined in the semiconducting material according to any of claims 2 to 17 when measured under the same conditions by cyclic voltammetry.

26. The electronic device of claim 24, wherein the light emitting layer comprises a light emitting polymer.

27. The electronic device of claim 24, wherein the light emitting layer is adjacent to an electron injecting or electron transporting layer.

28. The electronic device of claim 24, wherein the light emitting layer emits blue or white light.

29. The electronic device of claim 24, wherein the cathode is a transparent conductive oxide cathode.

30. The electronic device of claim 24, which is a tandem OLED stack.